The problem isn't that it's pinging at cruise, it's when I accelerate from cruising. Like If i tip into the throttle a little to speed up. It dosn't do it going uphill either, it's got to be a light acceleration like I'm going to pass someone, but not in a hurry. And it's a very light detonation sound that only lasts for a second. If I hammer it off cruise, I might get one ping if even at all. It doesn't ping any at WOT which I think it would do if it was too lean, that's why I'm thinking vac advance.

This probably shows the mixture drops lean when the throttle is opened, this is common with a big cam as the air flow dies momentarily and fuel falls out of suspension. With no continuance of detonation once mixture velocity picks up, I'd say you need more accelerating shot and maybe the power valve needs to come in sooner (i.e. a higher vacuum).

You will, also, have to figure out if the secondary opening drops the mixture lean as well; although vacuum secondaries tend to be more graceful than mechanical in this regard, it still could be a problem. The Q-jet suffered in some applications with this to where they put enrichment ports just above the closed air valve so when it would start to open it would pull some extra fuel. Holley, of course, has the "famous" double pumper for the same reason. You could either add this feature if it isn't on the carb, or increase the secondary metering a couple jet sizes, or put in a stiffer spring to slow the secondary actuation a bit.